PROJECT SUMMARY Focal segmental glomerulosclerosis (FSGS) is a significant cause of chronic kidney disease, has few effective treatment options, and usually progresses to end-stage renal disease (ESRD). FSGS has a substantive genetic component. Study of gene mutations that cause FSGS has provided invaluable insight into normal glomerular function and the disease pathogenesis of FSGS. Mutations in TRPC6 are a known cause of FSGS. In addition, TRPC6 levels are often increased in more common forms of kidney disease, implying that TRPC6 activity may impact both acquired and genetic forms of FSGS. TRPC6 is an ion channel found on the surface of cells, making it an attractive pharmacologic target. However, two key questions about TRPC6 and the development of FSGS remain unanswered. Is it simply that excess TRPC6 activity is detrimental to glomerular function, or is TRPC6 like Goldilocks, with either too much or too little detrimental? Which of the multiple signaling pathways intersecting with TRPC6 are relevant to the development of glomerular pathology? We have created novel animal models - mice with the equivalent of a human FSGS mutation in Trpc6 and others with a dominant negative (DN) Trpc6 mutation - to be able to address these questions. Our experimental plan has three Specific Aims with the goal of providing answers to the above questions: (1) To ascertain whether mice with FSGS- or DN-mutations in Trpc6 develop FSGS with age or require a ?second hit? to manifest disease. (2) To characterize the effect of TRPC6 mutations on podocyte behaviors known to be affected in FSGS, focusing on regulation of their actin cytoskeleton, calcineurin-NFAT signaling, and cell death. (3) To determine the genes necessary for mutant TRPC6-induced cell death. Our proposed studies have the potential to significantly enhance our understanding of FSGS. They will help us understand how increased and decreased TRPC6 activity alters glomerular response to stress, and will clarify which of the known signaling pathways activated by TRPC6 mediate pathology. The research has the potential to uncover novel molecular mechanisms involved in regulating TRPC6 and promoting FSGS. Ultimately, the results will help determine whether blocking TRPC6 activity might be a potential, and much needed, new therapeutic approach for the treatment of FSGS.